To some extend you do and it makes a difference. The O2 pressure in air is about 0.2 bar (~3 psi) while it is 1.0 bar (~15 psi) in pure O2. As a result you cannot overaerate with air and at common pitching teemps air saurated water wort is likely around 8-10 ppm. This is different with pure O2 where you can actually overoxygenate the wort. But pure O2 also allows you to get sufficient O2 into high graviy worts where you are limited with the use of air.

I had built an inline aeration contraption out of PVC, using a bit of tubing and silicone caulk to attach my barbed aeration stone to the gadget. Drawbacks: couldn't bring the PVC above ~150, so had to permanently store it in sanitizing solution, and the caulking just didn't stick well enough, and the tubing popped off with the aeration stone. But for the $3 in PVC it cost me, good learning experience

I just rebuilt the contraption out of copper, should be far more solid now, and you can remove the aeration 'insert' for the lack of a better word, whereas the PVC one I made was more enclosed. Just finished it yesterday, and more of an initial prototype. Brewing today, so we'll see how it works. The only not as solid as it could be part was joining the barbed aeration stone to the 3" nipple. I tried using copper solder, no luck, it won't stick to the stainless, and didn't want to try brazing the stainless onto the brass as I don't know if that would work nor whether the stone itself would handle that kind of heat, so I used a bit of JB weld and shoved the barb inside the nipple. We'll see if it holds.

Q1: But I do have a couple questions for you guys: where the crap do you find the aeration stones with threads? No matter where I look or how much searching I do, I can only find the ones with barbs. However, if I were to make one again, I'm going to order a stainless steel 1/8" x 3" nipple so that I could shove the barb end inside it, and weld it together, the SS nipple was probably only a buck more than the brass one.

Q2: And since I enjoy making this type of stuff and providing custom equipment to my fellow home brewers, how many of you would like to have an inline aeration gadget? Would $60 + cost of aeration stone (as this is the big unknown) be reasonable? If interest is high enough, I'll make another one.

Back to the original thread: oxygen; too much or not enough. I'm using an oxygen tank, and my method (to some bit of madness) was to start the oxygenation while I was still doing the recirculation of the wort through the CFC bringing it down to the final temp about a minute before I move to dumping it into the fermenter. Doing about 5 PSI using a 2 micron aeration stone. I get a nice milky color out of the wort.

However, like bo_gator (the original poster) I admit I have no idea if this is too little or too much, as all of the batches I've used this contraption in are still in the garage in kegs untapped. So before I get to drinking those..

Those of you who already use some sort of an inline aeration gadget, at what point do you begin your aeration, at what PSI and what micron level (and even the overall size) is your stone?

Obviously, too little oxygen means bad attenuation.

Too much oxygen, what would be the perceived effects? That way I know what to look for when I actually tap those kegs.

I'm considering going to a pump with a sanitary filter to push in plain old air, and as Kai pointed out, it's impossible to over oxygenate with that method, though O2 may still be better for a big beer. For those of you who use this method, what pumps do you use to force air in, and which do you like best?

Has anyone experimented with "intermittent" aeration during early fermentation?

By this I mean occasionally aerating the wort with air pumped through a sterile filter. This would be through a pre-drilled hole in a bucket lid, so no need to worry about repeated risk of infection.

The point would be to potentially make up for the limits of the initial aeration of this system (say 8 - 10 ppm), to use on bigger beers, and do it (for example) for ten minutes twice a day up to the point of high krausen starting to form (or before). In red wine making for example, many authors say to not create an airtight primary so as to ensure oxygen for yeast, and of course there are all the commercial breweries that use open fermentation. I don't have such a sanitary condition in my basement, so that's a risky option to say the least...

A post Kai made in another thread got me thinking about this. His original post was in regards to the good results he had from continual aeration of starter wort (although I don't remember that he performed a taste test

A post Kai made in another thread got me thinking about this. His original post was in regards to the good results he had from continual aeration of starter wort (although I don't remember that he performed a taste test

Constantly aerating the yeast during propagation is different since the resulting beer is discarded. It may actually enable you to skip aeration of the wort that the yeast is pitched into. I haven’t tried that yet.

But early aeration of high gravity beers is certainly worth a try. You may want to watch out for a massive blow-off caused by the CO2 release when you introduce a lot of small air bubbles. A series of short 1-2s air bursts every 1-2 min might be better for controlling that blow-off